Metal organic framework derived carbon coated iron-cobalt alloy catalyst as well as preparation method and application thereof

Abstract

The invention discloses a metal organic framework derived carbon coated iron-cobalt alloy catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: preparing an iron-based metal organic framework, phenanthroline, cobalt salt and an organic solvent into a precursor mixed solution, and performing solvothermal reaction and pyrolysis to obtain the iron-cobalt alloy catalyst. According to the preparation method disclosed by the invention, cheap and easily available raw materials are adopted, and the green and environment-friendly metal organic framework derived carbon coated iron-cobalt alloy catalyst which is large in specific surface area, rich in active sites, stable in structure and excellent in catalytic performance can be prepared through a mild solvent volatilization-calcination two-step method; the method can be used for advanced treatment of organic pollutant wastewater, can realize efficient removal of organic pollutants, and is high in use value and good in application prospect. According to the preparation method disclosed by the invention, the iron-based metal organic framework is directly used as an iron source, so that additional addition of iron salt is avoided, the risk of iron precipitation and impurity introduction is fundamentally eliminated, and pH regulation is not needed.

Description

Technical Field

[0001] The invention belongs to the technical field of material preparation and persulfate activation, and relates to a metal organic framework-derived carbon-coated iron-cobalt alloy catalyst, a preparation method and an application thereof. Background Art

[0002] The increasingly serious environmental pollution problem in the world, especially the damage to aquatic ecosystems caused by organic wastewater discharged from industrial production, has posed a serious threat to human health and biodiversity. There is an urgent need to develop efficient wastewater treatment technologies. Among the many water treatment solutions, advanced oxidation processes (AOPs) based on persulfate (such as potassium permonosulfate, PMS) are highly favored due to their high cost-effectiveness and outstanding treatment efficiency. This technology activates PMS to produce sulfate radicals (SO4 ·- ) and hydroxyl radicals (·OH), which can efficiently degrade various organic pollutants and have become a research hotspot in the field of environmental governance in recent years.

[0003] Iron and cobalt are the most effective transition metals for activating hydrogen peroxide and PMS, respectively. Bimetallic catalysts, such as iron-cobalt alloys (FeCo alloys), can efficiently activate PMS by utilizing electron cycles formed by metal valence state transitions and are widely used in treating organic wastewater. However, FeCo alloys suffer from limitations such as particle agglomeration and the leaching of metal ions, particularly the highly toxic cobalt metal. These drawbacks significantly hinder their further application. Therefore, improving the catalytic activity of FeCo alloys while reducing metal leaching rates is a hot topic of research for scholars both domestically and internationally.

[0004] Metal-organic frameworks (MOFs), a class of porous crystalline coordination polymers with high specific surface areas, have become a research hotspot in recent years. Given their stable carbon skeletons, MOFs have also been reported as excellent supports for metal loading. However, the following defects still exist in iron-cobalt alloy catalysts prepared by calcining MOFs as support raw materials: (a) Part of the iron-cobalt alloy is exposed outside the carbon skeleton, which still poses a risk of metal ion leaching during actual application; (b) the nitrogen precursor used is corrosive and easily destroys the original structure of the carbon skeleton during calcination, resulting in poor catalyst stability; and (c) the poor electrical conductivity between the carbon material and the iron-cobalt alloy leads to low electron transfer efficiency, making it difficult to improve the catalytic efficiency of the catalyst. The existence of these defects makes it difficult for existing metal-organic framework-derived carbon-coated iron-cobalt alloy catalysts to efficiently activate persulfate, and thus to effectively degrade various organic pollutants.

[0005] Therefore, how to obtain a metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst with a large specific surface area, rich active sites, stable structure, excellent catalytic performance, and green environmental protection plays an important role in achieving efficient activation of persulfate and achieving efficient degradation of various organic pollutants under the premise of being more green and environmentally friendly. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst with large specific surface area, rich active sites, stable structure, excellent catalytic performance, and green environmental protection, as well as its preparation method and application.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A method for preparing a metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst comprises the following steps:

[0009] S1, mixing an iron-based metal organic framework, o-phenanthroline, a cobalt salt, and an organic solvent, and stirring to obtain a precursor mixture;

[0010] S2, performing a solvothermal reaction on the precursor mixture obtained in step S1 to obtain a precursor complex;

[0011] S3. Pyrolyzing the precursor complex obtained in step S2 to obtain a metal organic framework-derived carbon-coated iron-cobalt alloy catalyst.

[0012] The above preparation method is further improved, in step S1, the mass ratio of the iron-based metal-organic framework to o-phenanthroline is 1:0.1-0.3.

[0013] The above preparation method is further improved, in step S1, the mass ratio of the iron-based metal-organic framework to the cobalt salt is 1:0.2-0.6.

[0014] The above preparation method is further improved in that in step S1, the mass volume ratio of the iron-based metal-organic framework to the organic solvent is 2 mg:1 mL.

[0015] The above preparation method is further improved. In step S1, the cobalt salt is cobalt nitrate hexahydrate; the organic solvent is N,N-dimethylformamide; the stirring is carried out at a speed of 300 r / min to 500 r / min; the stirring time is 0.5 h; and the iron-based metal-organic framework is prepared by solvent thermal reaction using trivalent iron salt and 1,4-benzoic acid as raw materials.

[0016] The above preparation method is further improved in that in step S2, the solvent thermal reaction is carried out at a temperature of 150° C. and the time of the solvent thermal reaction is 18 hours.

[0017] The above preparation method is further improved. In step S3, the pyrolysis is carried out under an argon atmosphere; the heating rate during the pyrolysis process is 5°C / min; the pyrolysis temperature is 700°C; the pyrolysis time is 2 hours; after the pyrolysis is completed, the following treatment is also included: soaking the pyrolysis product in an acid solution, and washing the soaked product with water until the pH value of the eluate is neutral; the soaking time is 2 hours; the acid solution is a hydrochloric acid solution; and the concentration of the acid solution is 1M.

[0018] As a general technical concept, the present invention also provides a metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst, which is prepared by the above-mentioned preparation method.

[0019] The above-mentioned metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst is further improved, wherein the metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst includes a metal-organic framework-derived carbon skeleton, iron-cobalt alloy nanoparticles are formed inside the metal-organic framework-derived carbon skeleton, and the surface of the iron-cobalt alloy nanoparticles is coated with a graphite carbon layer to form a core-shell structure.

[0020] The above metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst is further improved in that the mass percentage of iron-cobalt alloy nanoparticles in the metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst is 0.71%.

[0021] As a general technical concept, the present invention also provides a use of the above-mentioned metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst in treating organic pollutants in water.

[0022] The above application is further improved, comprising the following steps: mixing a metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst and organic pollutant wastewater, stirring, adding persulfate for catalytic reaction, and completing the treatment of the organic pollutant wastewater; the amount of the metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst added is 0.05g to 0.2g per liter of the organic pollutant wastewater; the amount of the persulfate added is 0.1mmol to 1mmol per liter of the organic pollutant wastewater.

[0023] The above application is further improved, wherein the persulfate is potassium monopersulfate; the concentration of organic pollutants in the organic pollutant wastewater is ≤10 mg / L; the organic pollutants in the organic pollutant wastewater are at least one of phenol, sulfamethoxazole, sulfamethazine, and para-chlorophenol; the metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst and the organic pollutant wastewater are mixed and stirred at a speed of 400 r / min to 600 r / min for 0.5 h to 1 h; and the catalytic reaction time is 1 min to 10 min.

[0024] Compared with the prior art, the advantages of the present invention are:

[0025] (1) In view of the shortcomings of existing metal organic framework derived carbon coated iron cobalt alloy catalysts, such as the carbon skeleton being easily destroyed, the poor conductivity between the carbon material and the iron cobalt alloy, and the easy leaching of metal ions, the present invention creatively proposes a preparation method of a metal organic framework derived carbon coated iron cobalt alloy catalyst, which uses an iron-based metal organic framework (MIL-88B (Fe)) as a precursor, 1,2-phenanthroline as a chelating agent, a nitrogen precursor, and a reducing agent, and prepares a precursor mixture by stirring. Then, a solvent thermal reaction is carried out with the assistance of an organic solvent. During the solvent thermal reaction, an 1,2-phenanthroline-cobalt nitrate chelate is formed and can gradually penetrate into the pores of the iron-based metal organic framework, and the chelate is promoted to chelate with the iron in the pores of the iron-based metal organic framework to form a uniformly dispersed Fe-Co precursor complex. Finally, the precursor complex is calcined. During the calcination process, the metal precursor is decomposed and reduced, and the 1,2-phenanthroline-cobalt nitrate chelate is formed in the pores of the iron-based metal organic framework. Under the strong coordination effect of o-phenanthroline and iron-cobalt, the formation of alloy nanoparticles is precisely regulated, and the iron-cobalt alloy nanoparticles are evenly encapsulated in the mesoporous channels of the iron-based metal-organic framework-derived carbon to form highly dispersed iron-cobalt alloy nanoparticles. At the same time, under the protection of o-phenanthroline, the high-temperature corrosion caused by the iron-cobalt alloy nanoparticles during the sintering process can be effectively inhibited. More importantly, during the calcination process, through the synergistic effect of chelation and confinement, o-phenanthroline can be carbonized to form a highly graphitized carbon layer and coated on the surface of the iron-cobalt alloy nanoparticles. On the one hand, the highly graphitized carbon layer can promote the electron transfer efficiency between the carbon skeleton and the iron-cobalt alloy nanoparticles, making the catalyst have better conductivity. On the other hand, the highly graphitized carbon layer can also effectively prevent metal ion leaching as a protective layer, which is more green and environmentally friendly. In particular, the chelation effect of o-phenanthroline can also promote the formation of highly dispersed iron-cobalt alloy nanoparticles in the carbon skeleton.Compared with conventional iron-cobalt catalysts, the metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst prepared by the present invention has the following significant advantages: (a) unique core-shell structure: a highly graphitized carbon layer is coated on the surface of the iron-cobalt alloy nanoparticles to form a unique core-shell structure, which can not only promote the improvement of the conductivity of the catalyst, but also prevent the leaching of the metal. At the same time, the iron-cobalt alloy nanoparticles coated with the graphitized carbon layer are confined in the MOF-derived porous carbon matrix, which can also effectively prevent metal agglomeration; (b) optimized interface characteristics: the high specific surface area of ​​the MOF-derived carbon provides a rich active site exposure interface, which promotes the mass transfer of reactants; (c) synergistic catalytic effect: under the promotion of the highly graphitized carbon layer, the carbon matrix and The electronic interaction of the iron-cobalt alloy is significantly enhanced, making the catalytic activity of the catalyst higher. At the same time, thanks to the difference in the electronic structure of iron and cobalt, the bimetallic system can form a significant synergistic effect, promote electron transfer and optimize the PMS activation path, thus having a higher activation efficiency for persulfate. When used to activate persulfate and degrade phenol, the process mainly generates long-lived active species such as singlet oxygen and free electrons, which can achieve a degradation rate of 100% for organic pollutants within 5 minutes, and can achieve efficient and continuous degradation of organic pollutants; (d) The MOF-derived carbon shell not only fixes the iron-cobalt alloy nanoparticles, but its porous channels can also serve as a nanoreactor, achieving the following functions through the spatial confinement effect: ① Enrichment of active species: the generated 1 Free radicals such as O2 are localized inside the pores, reducing their non-target consumption with background substances in the water body (such as natural organic matter, anions, etc.); ② Enhanced mass transfer efficiency: The confined environment of the pores can prolong the life of active species and promote the contact frequency between pollutant molecules and active sites. In the preparation method of the present invention, cheap and readily available raw materials are used, and a metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst with a large specific surface area, rich active sites, stable structure, excellent catalytic performance, and green environmental protection can be prepared through a mild solvent volatilization-calcination two-step method. As a new type of catalyst with excellent performance, it can be used as an efficient PMS activator, and can deeply treat organic pollutant wastewater, as well as achieve efficient removal of organic pollutants, with high use value and good application. In addition, in the preparation method of the present invention, the iron-based metal-organic framework (MIL-88B (Fe)) is directly used as the iron source to avoid the additional addition of iron salts, fundamentally eliminating the risk of iron precipitation and impurity introduction, and no pH control is required. In the traditional method, Fe 2+ It is easy to precipitate under neutral conditions and requires frequent pH adjustment to maintain solubility.

[0026] (2) In the preparation method of the present invention, by optimizing the mass ratio of the iron-based metal organic framework to o-phenanthroline to 1:0.1-0.3, it is beneficial to prepare a metal organic framework-derived carbon-coated iron-cobalt alloy catalyst with better catalytic performance. This is because: when o-phenanthroline is not added or the amount is too low, the iron and cobalt are basically removed after acid washing, and the active sites are insufficient, resulting in reduced catalytic performance; when the amount of o-phenanthroline is too high, o-phenanthroline may chelate with iron and cobalt respectively to form independent metal complexes, and may agglomerate due to the high content to block the pores of the metal organic framework, which is not conducive to the formation of metal alloys during the reaction, resulting in the inhibition of catalytic performance.

[0027] (3) The present invention also provides an application of a metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst in treating organic pollutants in water bodies, specifically, the metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst and organic pollutant wastewater are mixed, stirred, and persulfate is added for catalytic reaction to complete the treatment of organic pollutant wastewater. In the present invention, the catalyst used produces strong oxidizing active species by activating persulfate, which can efficiently degrade organic pollutants in water bodies. Compared with traditional Fenton catalysts, this catalytic system shows significant advantages: rapid degradation reaction can be achieved under normal temperature and pressure conditions, and the catalyst has excellent cyclic stability and extremely low metal leaching characteristics, wherein the metal leaching of iron and cobalt is 70μg / L and 3.83μg / L respectively, both below the emission limit, and will not cause secondary pollution. Due to the use of environmentally friendly iron-based materials and renewable carbon carriers, the catalytic system not only has low operating costs, but also avoids the risk of secondary pollution, providing an efficient and green solution for deep treatment of industrial wastewater and drinking water safety, and has important environmental engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0029] Figure 1 These are scanning electron micrographs of the iron-based metal-organic framework (a), the iron-based metal-organic framework-coated o-phenanthroline-cobalt nitrate catalyst (b), and the metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst (c) prepared in Example 1 of the present invention.

[0030] Figure 2 The metal organic framework derived carbon coated iron cobalt alloy catalyst (FeCo@N 0.2 C), the metal organic framework derived carbon coated iron catalyst (Fe@N 0.2C), transmission electron micrographs of the iron / carbon catalyst (Fe@C) prepared in Comparative Example 2, and the metal organic framework-derived carbon-supported iron-cobalt alloy catalyst (FeCo@pyy) prepared in Comparative Example 3.

[0031] Figure 3 The metal organic framework derived carbon coated iron cobalt alloy catalyst (FeCo@N 0.2 C) high-resolution transmission electron microscopy images (ae) and X-ray energy spectrum (f).

[0032] Figure 4 The iron-based metal organic framework (MIL-88B(Fe)), the iron-based metal organic framework coated o-phenanthroline-cobalt nitrate catalyst (o-phen / Co-MIL-88B(Fe)), and the metal organic framework derived carbon coated iron cobalt alloy catalyst (FeCo@N 0.2 C) X-ray diffraction pattern.

[0033] Figure 5 The iron-based metal organic framework (MIL-88B(Fe)) and the metal organic framework-derived carbon-coated iron-cobalt alloy catalyst (FeCo@N 0.2 C), metal organic framework derived carbon-coated iron catalyst (Fe@N 0.2 C), iron / carbon catalyst (Fe@C), and metal-organic framework-derived carbon-supported iron-cobalt alloy catalyst (FeCo@pyy) for the activation of PMS for phenol in water.

[0034] Figure 6 This is a time-efficiency diagram of phenol in water with different pH values ​​when the metal organic framework-derived carbon-coated iron-cobalt alloy catalyst activates PMS in Example 3 of the present invention.

[0035] Figure 7 This is a diagram showing the degradation effect of phenol in water when the metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst in Example 4 of the present invention is activated with different concentrations of PMS.

[0036] Figure 8 This is a diagram showing the degradation effect of phenol in activated PMS-treated water under different concentration conditions using the metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst of Example 5 of the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0038] Example 1:

[0039] A method for preparing a metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst comprises the following steps:

[0040] (1) 10 mmol of ferric chloride hexahydrate and 10 mmol of 1,4-benzoic acid were added to 50 mL of N,N-dimethylformamide at room temperature and mixed well. Then, 4 mL of a 2 M sodium hydroxide aqueous solution was gradually added and stirred at 390 r / min for 30 minutes to obtain a mixed solution. The mixed solution was transferred to a 100 mL polytetrafluoroethylene autoclave and heated in an oven at 100°C for 12 hours. After natural cooling, the mixed solution was washed with N,N-dimethylformamide and ethanol. The fresh slurry was separated by centrifugation. The solid was collected by centrifugation and dried in a vacuum oven at 60°C for 12 hours to obtain an iron-based metal-organic framework, designated as MIL-88B(Fe).

[0041] (2) 500 mg of MIL-88B(Fe), 100 mg of o-phenanthroline and 250 mg of cobalt nitrate hexahydrate were added to 25 mL of N,N-dimethylformamide and stirred for 30 min to mix evenly to obtain a mixed solution. The mixed solution was transferred to a 100 mL polytetrafluoroethylene autoclave and placed in an oven for solvothermal heating at 150 ° C for 18 h. During this process, the o-phenanthroline-cobalt nitrate chelate was uniformly dispersed in the MOF pores with the assistance of an organic solvent. After natural cooling, the fresh slurry was centrifuged and washed with N,N-dimethylformamide and ethanol. The solid was collected by centrifugation and vacuum dried at 60 ° C for 12 h. The solid was pulverized in an agate mortar to obtain a precursor complex, which is an iron-based metal organic framework-coated o-phenanthroline-cobalt nitrate catalyst, recorded as o-phen / Co-MIL-88B(Fe).

[0042] (3) Place the precursor complex obtained above into the ark and heat it at a rate of 5°C min -1 , the temperature was raised to 700 ° C in an argon atmosphere and pyrolyzed for 2 h. After pyrolysis, the material was washed with 1 M hydrochloric acid aqueous solution for 2 h, washed with water until neutral (the eluate was neutral), and vacuum dried at 60 ° C for 12 h to obtain a metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst, which is an iron-based metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst, recorded as FeCo@N 0.2 C.

[0043] In this example, the metal organic framework-derived carbon-coated iron-cobalt alloy catalyst prepared under different o-phenanthroline conditions was also investigated. 0.2The preparation methods of C are basically the same, with the only difference being that the mass ratio of the iron-based metal-organic framework to o-phenanthroline is 1:0 (i.e., no o-phenanthroline is added), 1:0.5, and 1:1. The corresponding metal-organic framework-derived carbon-coated iron-cobalt alloy catalysts are denoted as FeCo@C, FeCo@N, and FeCo@C, respectively. 0.5 C, FeCo@N1C.

[0044] Comparative Example 1:

[0045] A method for preparing a metal-organic framework-derived carbon-coated iron catalyst is substantially the same as the preparation method of Example 1, except that cobalt nitrate hexahydrate is not added in Comparative Example 1.

[0046] The metal organic framework derived carbon-coated iron catalyst prepared in Comparative Example 1 is denoted as Fe@N 0.2 C.

[0047] Comparative Example 2:

[0048] A preparation method of an iron / carbon catalyst is substantially the same as the preparation method of Example 1, except that cobalt nitrate hexahydrate and o-phenanthroline are not added in Comparative Example 2.

[0049] The iron / carbon catalyst prepared in Comparative Example 2 is denoted as Fe@C.

[0050] Comparative Example 3:

[0051] A method for preparing a metal-organic framework-derived carbon-supported iron-cobalt alloy catalyst is substantially the same as the preparation method of Example 1, except that in Comparative Example 3, 310 μL of pyrrole is used instead of 100 mg of o-phenanthroline in Example 1.

[0052] The metal organic framework-derived carbon-supported iron-cobalt alloy catalyst prepared in Comparative Example 3 is denoted as FeCo@pyy.

[0053] Figure 1 The following are scanning electron micrographs of the iron-based metal organic framework (a), the iron-based metal organic framework-coated o-phenanthroline-cobalt nitrate catalyst (b), and the metal organic framework-derived carbon-coated iron-cobalt alloy catalyst (c) prepared in Example 1 of the present invention. Figure 1 (a) It can be seen that the prepared iron-based metal-organic framework (MIL-88B(Fe)) exhibits a typical spindle-shaped morphology with an uneven size distribution; Figure 1 (b) shows that after impregnation treatment, the iron-based metal organic framework coated o-phenanthroline-cobalt nitrate catalyst (o-phen / Co-MIL-88B(Fe)) can still maintain its original spindle structure well, but there is a slight agglomeration phenomenon; Figure 1(c) The metal organic framework derived carbon coated iron cobalt alloy catalyst (FeCo@N 0.2 C) Metal particles are formed inside the derived carbon, and these nanoparticles are almost completely covered by the derived carbon layer.

[0054] Figure 2 The metal organic framework derived carbon coated iron cobalt alloy catalyst (FeCo@N 0.2 C), the metal organic framework derived carbon coated iron catalyst (Fe@N 0.2 C), transmission electron micrographs of the iron / carbon catalyst (Fe@C) prepared in Comparative Example 2, and the metal organic framework-derived carbon-supported iron-cobalt alloy catalyst (FeCo@pyy) prepared in Comparative Example 3. Figure 2 In the equation, a is Fe@C and b is Fe@N. 0.2 C, c is FeCo@pyy, d is FeCo@N 0.2 C. From Figure 2 It can be found that in the catalyst prepared by o-phenanthroline, the metal nanoparticles are all wrapped by a dense layer of graphitic carbon, which shows that the presence of o-phenanthroline provides a key precursor for the formation of the graphitic carbon protective layer. Through its unique molecular structure and pyrolysis behavior, it promotes the formation of a highly graphitized carbon layer, thus creating these graphitic carbon protective layers with excellent conductivity and stability.

[0055] Figure 3 The metal organic framework derived carbon coated iron cobalt alloy catalyst (FeCo@N 0.2 C) high-resolution transmission electron microscopy images (ae) and X-ray energy spectrum (f). Figure 3 As can be seen in (ae), the metal alloy particles present a unique core-shell structure: the core is metal alloy, the middle is a highly graphitized carbon layer, and the outer layer is amorphous carbon. Figure 3 (f) shows that the C and O elements are evenly distributed in the composite material, and the overlapping distribution of Fe and Co elements confirms the formation of FeCo alloy.

[0056] Figure 4 The iron-based metal organic framework (MIL-88B(Fe)), the iron-based metal organic framework coated o-phenanthroline-cobalt nitrate catalyst (o-phen / Co-MIL-88B(Fe)), and the metal organic framework derived carbon coated iron cobalt alloy catalyst (FeCo@N 0.2 C) X-ray diffraction pattern. Figure 4It can be seen that there are relatively obvious peaks at 2θ = 21.0°, 26.4°, 44.8°, 65.2° and 82.6°. The first two correspond to the (100) and (002) crystal planes of carbon (JCPDS card number 41-1487), and the last three peaks correspond to FeCo alloys, respectively. Among them, the diffraction peak with the strongest intensity is the (110) crystal plane, which is consistent with JCPDS card number 49-1568.

[0057] Example 2:

[0058] A metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst is used in treating organic pollutant wastewater, specifically using the metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst to activate persulfate to degrade phenol in water, comprising the following steps:

[0059] The iron-based metal organic framework (MIL-88B(Fe)) and the metal organic framework-derived carbon-coated iron-cobalt alloy catalyst (FeCo@N 0.2 C), the metal organic framework derived carbon coated iron catalyst (FeCo@C, Fe@N 0.2 C, FeCo@N0.5C, FeCo@N1C), the iron / carbon catalyst (Fe@C) prepared in Comparative Example 2, and the metal organic framework-derived carbon-supported iron-cobalt alloy catalyst (FeCo@pyy) prepared in Comparative Example 3, 10 mg each, were placed in 50 mL of a phenol solution (pH 6.8) with a concentration of 10 mg / L, placed on a magnetic stirrer, set the stirring speed to 450 r / min, stirred for 20 min, and potassium permonosulfate (chemical formula 2KHSO5·KHSO4·K2SO4, i.e., PMS) was added, the concentration of PMS in the system was 0.50 mM, and the catalytic reaction was carried out under natural light to achieve the degradation of phenol in water.

[0060] During the catalytic process, 1 mL of phenol solution was taken at intervals of 1 min, 3 min, 5 min, and 10 min, filtered through a 0.22 μm filter membrane, and the concentration of the characteristic peak of phenol at 270 nm was detected by high performance liquid chromatography. The concentrations of MIL-88B (Fe) and FeCo@N prepared in Example 1 at different times were calculated. 0.2 C. Fe@N prepared in Comparative Example 1 0.2 The degradation efficiency of Fe@C prepared in C, Comparative Example 2 and FeCo@pyy prepared in Comparative Example 2 on phenol is shown in the following table. Figure 5 shown.

[0061] Figure 5 The iron-based metal organic framework (MIL-88B(Fe)) and the metal organic framework-derived carbon-coated iron-cobalt alloy catalyst (FeCo@N0.2 C), metal organic framework derived carbon-coated iron catalyst (Fe@N 0.2 C), iron / carbon catalyst (Fe@C), and metal-organic framework-derived carbon-supported iron-cobalt alloy catalyst (FeCo@pyy) for the activation of PMS for phenol in water. Figure 5 The results showed that within 10 min, the catalytic activity of the synthesized MIL-88B(Fe) on PMS was weak, and the removal rate of phenol was only about 8.67%. 0.2 In the C / PMS and FeCo@pyy / PMS systems, the removal effect of phenol increased but was not completely removed, with removal rates of approximately 51.05%, 63.23%, and 78.69%, respectively, while the FeCo@N 0.2 The degradation efficiency of phenol by FeCo@C was as high as 100% within 5 min. In addition, under the same conditions, the degradation efficiency of phenol by FeCo@C, FeCo@N0.5C and FeCo@N1C within 5 min was 32.1%, 79.7% and 68.6% respectively. 0.2 The degradation efficiency of C on sulfamethoxazole, sulfamethazine and p-chlorophenol reached 100% within 5 minutes.

[0062] Example 3:

[0063] The effect of the metal organic framework derived carbon coated iron cobalt alloy catalyst on the degradation of phenol in activated PMS treated water at different pH values ​​was investigated. Specifically, the FeCo@N prepared in Example 1 of the present invention was used. 0.2 C activated PMS treatment of phenol in water, comprising the following steps:

[0064] The metal organic framework derived carbon coated iron cobalt alloy catalyst (FeCo@N 0.2 C), 10 mg each, were placed in phenol solutions with pH values ​​of 3, 5, 9, and 11 (the volume of these solutions was 50 mL and the concentration was 10 mg / L), placed on a magnetic stirrer, set the stirring speed to 450 r / min, stirred for 20 minutes, and PMS was added to make the concentration of PMS in the system 0.50 mM. The catalytic reaction was carried out under natural light to achieve the degradation of phenol in water.

[0065] During the catalytic process, 1 mL of phenol solution was collected at intervals of 1 min, 3 min, 5 min, and 10 min, filtered through a 0.22 μm filter membrane, and the concentration of the phenol corresponding characteristic peak at 270 nm was detected by high performance liquid chromatography. The degradation efficiency of phenol in water with different pH values ​​over the metal organic framework-derived carbon-coated iron-cobalt alloy catalyst at different times was calculated. The results are shown in the figure. Figure 6 shown.

[0066] Figure 6 This is a time-efficiency diagram of phenol in water with different pH values ​​when the metal organic framework-derived carbon-coated iron-cobalt alloy catalyst activates PMS in Example 3 of the present invention. Figure 6 The pH value of Control is 6.8. Figure 6 The catalytic degradation performance test results show that the metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst of the present invention exhibits excellent catalytic performance in a wide pH range. When the initial pH value of the reaction system varies in the range of 3 to 11, the degradation efficiency of the catalyst for phenol wastewater always remains at a high level, which indicates that the catalyst has good pH adaptability and stable catalytic activity. It is particularly noteworthy that under strongly acidic (pH = 3) and weakly alkaline (pH = 11) conditions, the catalyst can still maintain satisfactory reaction activity, and its degradation efficiency does not show a significant decrease compared with that under neutral conditions. This feature is significantly better than the dependence of traditional Fenton catalysts on strongly acidic environments.

[0067] Example 4:

[0068] The effect of the metal organic framework derived carbon coated iron cobalt alloy catalyst on the degradation of phenol in activated PMS treated water was investigated under different concentrations of PMS solution. Specifically, the FeCo@N prepared in Example 1 of the present invention was used. 0.2 C activated PMS treatment of phenol in water, including the following steps:

[0069] Four portions of the metal organic framework derived carbon-coated iron-cobalt alloy catalyst (FeCo@N 0.2 C), 10 mg of each portion was placed in 50 mL of a 10 mg / L phenol solution (pH 6.8), placed on a magnetic stirrer, set the stirring speed to 450 r / min, stirred for 20 minutes, and PMS was added respectively to make the concentration of PMS in the system 0.10 mM, 0.25 mM, 0.50 mM, and 1.00 mM, respectively. The catalytic reaction was carried out under natural light to achieve the degradation of phenol in water.

[0070] During the catalytic process, 1 mL of phenol solution was collected at intervals of 1 min, 3 min, 5 min, and 10 min, filtered through a 0.22 μm filter membrane, and the concentration of the phenol corresponding characteristic peak at 270 nm was detected by high performance liquid chromatography. The degradation efficiency of phenol in water by the metal organic framework-derived carbon-coated iron-cobalt alloy catalyst under different PMS concentration conditions was calculated. The results are as follows: Figure 7 shown.

[0071] Figure 7The figure shows the degradation effect of phenol in water when the metal organic framework derived carbon coated iron cobalt alloy catalyst activates different concentrations of PMS in Example 4 of the present invention. Figure 7 As can be seen, the decomposition rate of phenol increases rapidly as the PMS concentration increases from 0.10 mM to 0.50 mM. This is because the more PMS molecules present during the reaction, the more PMS available for activation and decomposition, and the more active species generated. However, when the PMS concentration further increases to 1.00 mM, the phenol degradation efficiency decreases abnormally. This may be due to the self-quenching effect of excess PMS in the reaction system, whereby the high concentration of PMS molecules reacts with each other, consuming some of the active free radicals, or the excess PMS competes with intermediates, inhibiting the degradation efficiency of the target pollutant.

[0072] Example 5:

[0073] The effects of metal organic framework derived carbon coated iron cobalt alloy catalyst on the degradation of phenol in activated PMS treated water were investigated under different catalyst concentrations. Specifically, FeCo@N prepared in Example 1 of the present invention was used. 0.2 C activated PMS treatment of phenol in water, including the following steps:

[0074] The metal organic framework derived carbon coated iron cobalt alloy catalyst (FeCo@N 0.2 C) were placed in 50 mL of a 10 mg / L phenol solution (pH 6.8), placed on a magnetic stirrer, set the stirring speed to 450 r / min, stirred for 20 minutes, and PMS was added to make the concentration of PMS in the system 0.50 mM. The catalytic reaction was carried out under natural light to achieve the degradation of phenol in the water.

[0075] During the catalytic process, 1 mL of phenol solution was taken at intervals of 1 min, 3 min, 5 min, and 10 min, filtered through a 0.22 μm filter membrane, and the concentration of the phenol corresponding characteristic peak at 270 nm was detected by high performance liquid chromatography. The degradation efficiency of phenol in water under different concentration conditions of the metal organic framework-derived carbon-coated iron-cobalt alloy catalyst was calculated. The results are shown in the figure. Figure 8 shown.

[0076] Figure 8 This is a graph showing the degradation effect of phenol in water treated with activated PMS under different concentration conditions using the metal organic framework derived carbon coated iron-cobalt alloy catalyst in Example 5 of the present invention. Figure 8As can be seen, increasing the catalyst dosage from 50 mg / L to 100 mg / L significantly improves the phenol removal efficiency and accelerates the reaction rate. However, further increasing the catalyst dosage to 200 mg / L slows the rate of improvement. Experimental results indicate that 100 mg / L is the optimal catalyst dosage concentration, under which the number of active sites in the reaction system reaches the optimal ratio, enabling complete phenol degradation within 5 minutes. This phenomenon can be explained by the fact that within the lower catalyst concentration range (50-100 mg / L), increasing the catalyst dosage linearly increases the number of active sites, promoting the generation of more active free radicals. However, when the catalyst concentration exceeds 100 mg / L, the increase in catalytic efficiency no longer follows a linear relationship with catalyst dosage due to the increased recombination probability of active free radicals in the reaction system and factors such as mass transfer limitations. Instead, the utilization of active sites may decrease.

[0077] From the above results, it can be seen that compared with conventional iron-cobalt catalysts, the metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst prepared by the present invention has the following significant advantages: (a) Unique core-shell structure: A highly graphitized carbon layer is coated on the surface of the iron-cobalt alloy nanoparticles to form a unique core-shell structure, which can not only promote the improvement of the conductivity of the catalyst, but also prevent the leaching of the metal. At the same time, the iron-cobalt alloy nanoparticles coated with the graphitized carbon layer are confined in the MOF-derived porous carbon matrix, which can also effectively prevent metal agglomeration; (b) Optimized interface characteristics: The high specific surface area of ​​MOF-derived carbon provides a rich active site exposure interface, which promotes the mass transfer of reactants; (c) Synergistic catalytic effect: The promotion effect of the highly graphitized carbon layer Under the condition of the carbon matrix, the electronic interaction between the carbon matrix and the iron-cobalt alloy is significantly enhanced, making the catalytic activity of the catalyst higher. At the same time, thanks to the difference in the electronic structure of iron and cobalt, the bimetallic system can form a significant synergistic effect, promote electron transfer and optimize the PMS activation path, so that the persulfate activation efficiency is higher. When used to activate persulfate and degrade phenol, the process mainly generates long-lived active species such as singlet oxygen and free electrons, which can achieve a 100% degradation rate of phenol within 5 minutes, and can achieve efficient and continuous degradation of organic pollutants; (d) The MOF-derived carbon shell not only fixes the iron-cobalt alloy nanoparticles, but its porous channels can also serve as a nanoreactor, achieving the following functions through the spatial confinement effect: ① Enrichment of active species: The generated 1Free radicals such as O2 are localized inside the pores, reducing their non-target consumption with background substances in the water body (such as natural organic matter, anions, etc.); ② Enhanced mass transfer efficiency: The confined environment of the pores can prolong the life of active species and promote the contact frequency between pollutant molecules and active sites. In the preparation method of the present invention, cheap and readily available raw materials are used, and a metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst with a large specific surface area, rich active sites, stable structure, excellent catalytic performance, and green environmental protection can be prepared through a mild solvent volatilization-calcination two-step method. As a new type of catalyst with excellent performance, it can be used as an efficient PMS activator, and can deeply treat organic pollutant wastewater, as well as achieve efficient removal of organic pollutants, with high use value and good application. In addition, in the preparation method of the present invention, the iron-based metal-organic framework (MIL-88B (Fe)) is directly used as the iron source to avoid the additional addition of iron salts, fundamentally eliminating the risk of iron precipitation and impurity introduction, and no pH control is required. In the traditional method, Fe 2+ It is easy to precipitate under neutral conditions and requires frequent pH adjustment to maintain solubility.

[0078] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions that fall within the scope of protection of the present invention are within the scope of protection of the present invention. It should be noted that improvements and modifications that can be made by a person skilled in the art without departing from the principles of the present invention are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a metal organic framework derived carbon-coated iron-cobalt alloy catalyst, characterized in that: The following steps are involved: S1, mixing an iron-based metal organic framework, o-phenanthroline, a cobalt salt, and an organic solvent, and stirring to obtain a precursor mixture; S2, performing a solvothermal reaction on the precursor mixture obtained in step S1 to obtain a precursor complex; S3. Pyrolyzing the precursor complex obtained in step S2 to obtain a metal organic framework-derived carbon-coated iron-cobalt alloy catalyst.

2. The preparation method according to claim 1, characterized in that In step S1, the mass ratio of the iron-based metal-organic framework to o-phenanthroline is 1:0.1-0.3; the mass ratio of the iron-based metal-organic framework to cobalt salt is 1:0.2-0.6; and the mass volume ratio of the iron-based metal-organic framework to organic solvent is 2 mg:1 mL.

3. The preparation method according to claim 2, characterized in that In step S1, the cobalt salt is cobalt nitrate hexahydrate; the organic solvent is N,N-dimethylformamide; the stirring is carried out at a rotation speed of 300 r / min to 500 r / min; the stirring time is 0.5 h; and the iron-based metal-organic framework is prepared by solvent thermal reaction using trivalent iron salt and 1,4-benzoic acid as raw materials.

4. The preparation method according to any one of claims 1 to 3, characterized in that In step S2, the solvent thermal reaction is carried out at a temperature of 150° C. and the solvent thermal reaction time is 18 hours.

5. The preparation method according to any one of claims 1 to 3, characterized in that In step S3, the pyrolysis is carried out under an argon atmosphere; the heating rate during the pyrolysis process is 5°C / min; the pyrolysis temperature is 700°C; the pyrolysis time is 2 hours; after the pyrolysis is completed, the following treatment is also included: soaking the pyrolysis product in an acid solution, and washing the soaked product with water until the pH value of the eluate is neutral; the soaking time is 2 hours; the acid solution is a hydrochloric acid solution; the concentration of the acid solution is 1M.

6. A metal organic framework derived carbon-coated iron-cobalt alloy catalyst, characterized in that: The metal organic framework-derived carbon-coated iron-cobalt alloy catalyst is prepared by the preparation method according to any one of claims 1 to 5.

7. The metal organic framework derived carbon-coated iron-cobalt alloy catalyst according to claim 6, characterized in that The metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst includes a metal-organic framework-derived carbon skeleton, iron-cobalt alloy nanoparticles are formed inside the metal-organic framework-derived carbon skeleton, and the surface of the iron-cobalt alloy nanoparticles is coated with a graphite carbon layer to form a core-shell structure; the mass percentage of the iron-cobalt alloy nanoparticles in the metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst is 0.71%.

8. Use of the metal organic framework derived carbon-coated iron-cobalt alloy catalyst according to claim 6 or 7 in treating organic pollutants in water.

9. The use according to claim 8, characterized in that The following steps are involved: A metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst and organic pollutant wastewater are mixed and stirred, and persulfate is added for a catalytic reaction to complete the treatment of the organic pollutant wastewater; the amount of the metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst added is 0.05g to 0.2g per liter of the organic pollutant wastewater; the amount of the persulfate added is 0.1mmol to 1mmol per liter of the organic pollutant wastewater.

10. The use according to claim 9, characterized in that The persulfate is potassium monopersulfate; the concentration of organic pollutants in the organic pollutant wastewater is ≤10 mg / L; the organic pollutants in the organic pollutant wastewater are at least one of phenol, sulfamethoxazole, sulfamethazine, and para-chlorophenol; the metal-organic framework-derived carbon-coated iron-cobalt alloy catalyst and the organic pollutant wastewater are mixed and stirred at a speed of 400 r / min to 600 r / min for 0.5 h to 1 h; the catalytic reaction time is 1 min to 10 min.

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